Multi-function solid oxide fuel cell bundle and method of making the same

ABSTRACT

A multi-function bundle having all of the basic support functions integrated therein can be used as a basic building block component, for example, in a fuel cell engine. The multi-function bundle is modular, easy to assemble, and able to withstand the physical and thermal shocks encountered in mobile applications. The multi-function bundle utilizes fully distributed fuel and oxidant supply systems which help to reduce temperature gradients throughout the array of fuel cells. The multi-function bundle may be comprised of a plurality of fuel cells, an oxidant supply system, a fuel supply system and a support structure which integrates the fuel cells, oxidant supply system, and fuel supply system into a single unit. The oxidant and fuel supply systems may be fully distributed. The fuel supply system may include one or more fuel feed tube assemblies which allow distributed internal fuel reformation and reduce temperature gradients throughout the array of fuel cells.

This application is a continuation of U.S. application Ser. No.10/804,925 entitled Multi-Function Solid Oxide Fuel Cell Bundle andMethod of Making the Same filed Mar. 19, 2004.

BACKGROUND OF THE INVENTION

The present invention relates generally to fuel cells and moreparticularly to a multi-function fuel cell bundle having all of thebasic support functions integrated therein.

Internal combustion engines have evolved to the point where advancementsare not effective because of fundamental limitations in the basictechnology. Several technologies (e.g., electric engines, hydrogenengines, gas/electric hybrid engines, fuel cell engines, etc.) have beenproposed as possible substitutes for the internal combustion engine. Ofthe proposed technologies, fuel cells perhaps offer the most attractivesolution for replacing the internal combustion engine. In addition toincreased efficiency and decreased pollution, fuel cells are capable ofusing the same fuel sources (e.g., gasoline, diesel, natural gas, etc.),and thus existing fuel distribution networks, that are currently used bythe internal combustion engine. Therefore, conversion to fuel cells is amore cost effective solution than the other proposed technologies.

A fuel cell combines fuel and air in an electrochemical reaction thatproduces both electricity and heat. Typically, a fuel cell is comprisedof an electrolyte sandwiched between two electrodes (i.e., positive andnegative terminals). The electrodes have pores that allow fuel, air, andreaction products to flow with minimal flow resistance. The electrodesare good electrical conductors (i.e., have minimal resistance) and mayalso act as catalysts to increase the rate of the electrochemicalreaction within the fuel cell.

Fuel cells are typically classified according to the type of electrolyteemployed. For example, proton exchange membrane fuel cells (PEMFC)typically use synthetic polymers as an electrolyte, phosphoric acid fuelcells (PAFC) use a phosphoric acid (similar to a car battery), moltencarbonate fuel cells (MCFC) typically use a molten alkali carbonate ofpotassium hydroxide solution, and solid oxide fuel cells (SOFC)typically use a solid ceramic made mostly of zirconia.

The type of fuel used by a fuel cell may vary. Generally, the fuel canbe any substance that is capable of being reacted with oxygen (i.e.,burned) and is capable of flowing through the porous electrodestructure. Gaseous hydrogen is typically the most desirable fuel for usewithin fuel cells. Because gaseous hydrogen is somewhat difficult anddangerous to transport, however, an adequate fuel distribution system isnot currently available for gaseous hydrogen. Distribution systems doexist, however, for common hydrocarbon fuels such as natural gas,gasoline, and diesel. These fuels are composed of particularcombinations of hydrogen and carbon (hence the name “hydrocarbon”).Gaseous hydrogen can be extracted from these hydrocarbon fuels for useby a fuel cell through a process called reformation.

Reformation generally refers to the conversion of common hydrocarbonfuel into a different form. One common type of reformation that isemployed is known as steam reformation. During steam reformation, wateris heated to a high temperature to form steam which is then mixed withthe hydrocarbon fuel. The water/steam (H₂O) provides a source of oxygenthat combines with the carbon in the hydrocarbon, to form CO₂ and CO.Thus, the reformation process produces CO₂, CO, and hydrogen. Althoughmost of the hydrogen is supplied by the hydrocarbon, a significantportion may come from the water/steam.

The fuel reformation process may be divided into two parts: partialreformation and final reformation. Partial reformation representsbreaking down (reforming) a long chain hydrocarbon fuel to a firstlevel. Final reformation represents breaking down (reforming) theparticular compound formed by partial reformation to a final reformedfuel.

The distinction between partial and final reformation can be made due tothe way the two parts of the reformation process are carried out.Partial reformation is typically performed by a partial reformer whichemploys a bed of suitable catalyst material such that the rate of heatabsorbed by the reforming fuel mixture does not exceed the level atwhich carbon will precipitate (i.e., so coking does not occur). Finalreformation is typically performed by a final reformer which has no heattransfer limitations and can therefore absorb heat at high rates withoutprecipitating carbon (i.e., without coking).

Although fuel cells offer a promising alternative to internal combustionengines, the application of fuel cell technology to create a viable fuelcell engine has proven to be very difficult. Each type of fuel cell hasinherent limitations which impede its adaptation for use as analternative to the internal combustion engine. For example, PEMFC's andPAFC's are classified as low-temperature fuel cells because they operateat approximately 180 degrees Fahrenheit and 360 degrees Fahrenheit,respectively. At these temperatures, the PEMFC and PAFC engines requireseparate, external hydrocarbon fuel reformation equipment to supplyreformation heat to the fuel. Typically, the reformation heat isextracted directly from the fuel, thus reducing engine efficiency.Furthermore, the additional weight and space needed to house theexternal reformation system make PEMFC and PAFC engines impractical asreplacements for internal combustion engines.

In contrast, SOFCs operate at approximately 1800 degrees Fahrenheit andare classified as high temperature fuel cells. SOFCs are capable ofproviding their own reformation heat. The reformation heat can beefficiently extracted from the SOFCs exhaust, or through convectionand/or radiation from the cell itself, thus offering improved efficiencyover PEMFC and PAFC engines and eliminating the need for externalreformation systems. Accordingly, SOFCs are more promising than PEMFCand PAFC engines for replacing the internal combustion engine.

Typical SOFCs are constructed in either a tubular or planarconfiguration. In a planar configuration, the electrolyte is sandwichedbetween two electrode “plates.” An inherent problem with the planarconfiguration is that, near the edges of the plates, the reactants (fueland air) are in close proximity to each other without an electrolytematerial to prevent the reactants from chemically combining (as opposedto electrochemically combining through the electrolyte). Thus, theplanar configuration requires sophisticated edge seals to prevent thereactants from chemically combining.

The tubular configuration eliminates the need for sophisticated edgeseals. In a simplified example, a tubular SOFC is formed by rolling thethin sheet-like layers of electrodes and electrolyte into a tube suchthat the edges at one end of the sheet-like layer meet the correspondingedges from the opposite end of the sheet-like layer. The result is acomposite tube that consists of three basic layers, where one of theporous electrodes (e.g. the fuel electrode) is on the outside of thecell, the other porous electrode (e.g., the oxidant electrode) is on theinside of the cell, and the electrolyte is sandwiched between the twoelectrodes. Typically, one end of the tube is closed to further reduceedge sealing problems.

During operation, fuel is supplied to the fuel electrode, whereas anoxidant (i.e., feed air or oxygen) is supplied to the oxidant electrode.The fuel and oxidant pass through the pores of their respectiveelectrodes and electrochemically react on the surface of theelectrolyte, thereby producing heat and electricity.

The configurations for various SOFCs and for various stationary SOFCgenerators are taught, for example, by Isenberg in U.S. Pat. No.4,490,444, Isenberg in U.S. Pat. No. 4,664,987, Makiel in U.S. Pat. No.4,640,875, Somers et al. in U.S. Pat. No. 4,374,184, and Singh et al. inU.S. Pat. No. 4,894,297. In all of these patents, an axially elongated,tubular air cathode has a solid oxide electrolyte deposited over it. Asmall radial segment which contains a deposit of interconnectionmaterial down the length of the tube is placed in contact with the airelectrode. A fuel anode forms an outer layer over the electrolytecompleting the fuel cell. A current collector felt with metal fibers maybe attached to the interconnection material. Other fuel cellconfigurations are also known, such as those taught by Isenberg, in U.S.Pat. No. 4,728,584.

One or more fuel cells may be grouped together to form a cell bundle.The current collector felt of each cell in the bundle may beelectrically connected to its neighbor in series and parallel. Forexample, the cells in each row may be connected in series to the othercells in that row. Each row may be then connected in parallel with theother rows in the cell bundle.

The generators discussed in the above-mentioned patents are typicallyused in stationary settings (for example, within a power plant) or aredesigned to provide power for relatively stable loads (for example inlarge marine applications that have a large hotel load). Thus, thesegenerators may not be easily adapted to withstand the physical shock(for example, caused by a bumpy road) and thermal shock (for example,caused by frequent load swings) encountered by an internal combustionengine for a transportation application.

Additionally, assembly of prior art SOFC generators is time consumingand complex, making their use as a replacement for the internalcombustion engine cost prohibitive. Typically, prior art SOFC generatorsmust be assembled from individual parts within the confines of a housingwhich surrounds the generator. Conventional assembly procedures requireexcessive handling of the fuel cells and require extra space in thegenerator housing for assembly clearance. To reduce assembly time, theindividual fuel cells may be combined to form a basic cell bundle priorto insertion into the generator housing. Multiple basic cell bundles maythen be combined to form a fuel cell stack within the generator housing.However, the assembly of the generator is further complicated becauseeach cell in the stack must be connected to, for example, an oxidantsupply, a fuel supply, cell supports, generator walls, recirculationtubing, exhaust tubing, combustion chambers, and an external fuelreformer, among others.

Another problem with prior art generators is that the fuel reformationsystems are not fully distributed (i.e., each cell within the cell stackis not directly coupled with the same amount of fuel reformation). Somecells may be cooled much more than others as a result of non-uniformfuel reformation. As a consequence, cells that do not transfer heat forfuel reformation may operate at a higher temperature than the cells thatdo transfer heat for fuel reformation. Thus, large variations intemperature may occur throughout the cell stack causing additionalthermal stresses within the generator and/or reducing the performance ofcertain cells.

Thus, there exists a need for a multi-function bundle having all of thebasic support functions integrated therein which can be used as acomponent in a fuel cell engine. A need also exists for a multi-functionbundle that is modular, easy to assemble, and able to withstand thephysical and thermal shocks encountered in a mobile application. Afurther need exists for a multi-function bundle that utilizes fullydistributed fuel reformation systems to eliminate temperature variationsthroughout the bundle and that overcomes the other limitations inherentin prior art.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to a multi-function bundlecomprised of a plurality of fuel cells, an oxidant supply system, a fuelsupply system, a fuel reformation system, and a support structure. Thesupport structure integrates the plurality of fuel cells, oxidant supplysystem, fuel supply system, and fuel reformation system into a singleunit.

Another aspect of the present invention relates to a multi-functionbundle comprised of an elongated annular fuel cell having an oxidantelectrode and a fuel electrode separated by an electrolyte. An oxidantfeed tube is operable to supply an oxidant to the oxidant electrode, afuel feed tube assembly is operable to supply fuel to the fuelelectrode, and a support structure is operable to integrate theelongated annular fuel cell, oxidant feed tube, and fuel feed tubeassembly.

Another aspect of the invention relates to a method for assembling amulti-function bundle comprised of attaching a cell spacer to aprimitive bundle of fuel cells, attaching a recirculation box to theprimitive bundle of fuel cells, combining a plurality of air feed tubeswith an exhaust/air distribution box to form a feed tube—exhaust/air boxassembly, attaching the feed tube—exhaust/air box assembly to theprimitive bundle of fuel cells, combining a fuel box with a cell andfuel feed spacer to form a fuel box—cell and fuel feed spacer assembly,and attaching the fuel box—cell and fuel feed spacer assembly to theprimitive bundle of fuel cells.

Another aspect of the present invention relates to a fuel cell stackcomprised of a plurality of multi-function bundles arranged in one ormore rows and columns, wherein each of the plurality of multi-functionbundles includes a plurality of fuel cells, an oxidant supply system, afuel supply system, a fuel reformation system, and a support structurefor enabling the plurality of fuel cells, the oxidant supply system, thefuel supply system, and the fuel reformation system to operate as anintegrated unit.

Another aspect of the present invention relates to a pressurecontainment vessel comprised of a base for supporting a plurality ofmulti-function fuel cell bundles and a cover having a side wall and adomed top, said domed top having one or more corrugations.

Another aspect of the present invention relates to a fuel cell enginecomprised of a pressure containment vessel, and one or moremulti-function fuel cell bundles.

Another aspect of the present invention relates to an assembly comprisedof an entrance leg, a return leg, and a support fin, wherein theentrance leg, return leg, and support fm form a counter-flow heatexchanger and wherein the entrance leg and the return leg define a flowpath for at least one of a fuel and an oxidant.

Another aspect of the present invention relates to a device forelectrically connecting two or more tubular fuel cells comprised of anelongated conductive strip having a first contact for coupling with anouter surface of a tubular first fuel cell and having a second contactfor coupling with an outer surface of a second tubular fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

To enable the present invention to be easily understood and readilypracticed, the present invention will now be described for purposes ofillustration and not limitation, in connection with the followingfigures wherein:

FIG. 1A is a perspective view of a multi-function bundle according toone embodiment.

FIG. 1B is an exploded view of the multi-function bundle of FIG. 1Aaccording to one embodiment.

FIG. 1C is a detailed view of the closed end of an SOFC of FIG. 1A withan oxidant feed tube inserted therein according to one embodiment.

FIG. 2A is a simplified view of an arrangement of a portion of amulti-function bundle according to another embodiment.

FIG. 2B is a detailed view of the open end of the single SOFC of FIG. 2Awith its cell extender attached and its associated oxidant feed tubeinserted therein.

FIG. 3A is a perspective view of a fuel feed tube assembly of themulti-function bundle of FIG. 1A according to one embodiment.

FIG. 3B is a top end view of the fuel feed tube assembly of FIG. 3Aaccording to one embodiment.

FIG. 4A is a perspective view of a fuel feed tube assembly of themulti-function bundle of FIG. 1A according to one embodiment.

FIG. 4B is a top end view of a fuel feed tube assembly of FIG. 4Aaccording to one embodiment.

FIGS. 5A-5C are perspective views of a portion of the fuel distributionsystem for one or more multi-function bundles according to oneembodiment.

FIG. 6A is a perspective view of a multi-function bundle of FIG. 1Aillustrating the different process zones according to one embodiment.

FIG. 6B is a cut-away view of the multi-function bundle of FIG. 6Aaccording to one embodiment.

FIG. 7A is a perspective view of a cell-to-cell electrical connectoraccording to one embodiment.

FIG. 7B is an end view of the cell-to-cell electrical connector of FIG.7A according to one embodiment.

FIG. 7C is an end view of the electrical connector of FIG. 7A betweentwo adjacent SOFCs.

FIGS. 7D is a perspective view of a cell-to-cell electrical connectoraccording to one embodiment.

FIG. 8A is a perspective view of a cell-to-cell electrical connectoraccording to another embodiment.

FIG. 8B is an end view of the cell-to-cell electrical connector of FIG.8A according to one embodiment.

FIG. 8C is an end view of the electrical connector of FIG. 8A betweenseveral SOFCs.

FIG. 8D is a perspective view of a cell-to-cell electrical connector ofFIG. 8A between several SOFCs.

FIG. 9A is a perspective view of a cell-to-cell electrical connectoraccording to another embodiment.

FIG. 9B is an end view of the cell-to-cell electrical connector of FIG.9A according to one embodiment.

FIG. 9C is an end view of the electrical connector of FIG. 9A betweentwo SOFCs.

FIG. 10A is a perspective view of a cell-to-cell electrical connectoraccording to another embodiment.

FIG. 10B is an end view of the cell-to-cell electrical connector of FIG.10A according to one embodiment.

FIG. 10C is an end view of the electrical connector of FIG. 10A betweentwo SOFCs.

FIG. 11 is the cut-away view of the multi-function bundle of FIG. 1Aillustrating cell-to-cell electrical connections according to oneembodiment.

FIG. 12 illustrates an operational process for assembling themulti-function SOFC bundle of FIG. 1 A according to one embodiment.

FIG. 13 is a cut-away side view of a fuel cell engine according to oneembodiment.

FIG. 14 is a partial top view of the fuel cell engine of FIG. 13 mountedon a truck chassis according to one embodiment.

FIG. 15 is an isometric view of a stack of multi-function fuel cellbundles and associated support structures for the fuel cell engine ofFIG. 13 according to one embodiment.

FIG. 16 illustrates the layout of the lower support structure of FIG. 15relative to the base of the pressure containment vessel of the fuel cellengine of FIG. 15 according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is a perspective view of a multi-function bundle according toone embodiment. The multi-function bundle 10 embodies all of the basicsupport functions for the fuel cells 13 in a single, integrated unit.For example, the multi-function bundle may embody one or more of thefollowing functions in a single, integrated unit: cell-to-cellelectrical connections, oxidant distribution, fuel distribution, fuelreformation, process exhaust, process gas recirculation, andoxidant/fuel combustion, among others. Accordingly, the multi-functionbundle 10 may be a modular unit that serves as a building block forbuilding larger assemblies, for example, a generator stack (as bestshown in FIG. 15). Thus, the multi-function bundle 10 reduces the effortneeded (and eliminates extra costs typically encountered) duringgenerator stack assembly and/or repair.

FIG. 1B is an exploded view of the multi-function bundle 10 of FIG. 1Aaccording to one embodiment. The multi-function bundle 10 is comprisedof a primitive bundle 12 of fuel cells 13, oxidant feed tubes 14 (whichmay be positioned within fuel cells 13), fuel feed tube assemblies 16(which may be positioned between and/or around fuel cells 13), arecirculation box 17, an exhaust/air distribution box (EAB) 18, a fuelbox 19, a cell and fuel feed spacer (CFF Spacer) 20, and a cell spacer29. The primitive bundle 12 may be comprised of a plurality of tubularsolid oxide fuel cells (SOFCs) 13 each having an electrolyte 25 placedbetween oxidant 24 and fuel 26 electrodes, and an interconnection 23contacting the oxidant electrode 24 (as best shown in FIG. 6B), theconstruction of which is well known in the art. The SOFCs 13 may beelectrically connected to each other using flexible electricalconnections 70, 72, 74 (not shown in FIG. 1B) that axially traverse eachSOFC 13. The SOFCs 13 may be connected in series and/or in parallelwithin the primitive bundle 12.

It should be noted that the term “primitive bundle” 12 as used hereinrefers to a group of electrically connected fuel cells 13 and the term“multi-function bundle” as used herein refers to a primitive bundle 12of fuel cells with fully distributed oxidant, fuel, and/or fuelreformation systems and an appropriate bundle support structure (e.g.17, 18, 19, etc.). The bundle support structure enables the primitivebundle 12 and the oxidant supply, fuel supply, and fuel reformationsystems to operate as an integrated unit. In one embodiment, the bundlesupport structure also provides separation and proper flow distributionbetween different process zones (as discussed in conjunction with FIG.6A) within each multi-function bundle 10 and between two or moremulti-function bundles 10, for example, when combined to form a stack.

As illustrated in FIG. 1B, the primitive bundle 12 is comprised ofthirty-six (36) SOFCs 13 arranged in a six-by-six (6×6) array. Thenumber of SOFCs 13 used in the primitive bundle 12, the arraydimensions, and the manner of electrically connecting the individualSOFCs 13 within the primitive bundle 12 may be altered while remainingwithin scope of the present invention. Additionally, other types of fuelcells may be used while remaining within the scope of the presentinvention.

In one embodiment, the tubular SOFCs 13 also provide a means of holdingthe multi-function bundle 10 together (i.e., end-to-end) and help toaccommodate thermal growth experienced by the multi-function bundle 10.However, other end-to-end support arrangements may be used whileremaining within the scope of the present invention. For example, tierods with thermal expansion characteristics similar to the SOFCs 13 maybe embedded between and around the SOFCs 13. The end-to-end supports maybe needed only during construction of the multi-function bundle 10,thus, the “embedded tie rods” may be made from a material thatdisintegrates when the multi-function SOFC bundle 10 is operated.

The multi-function bundle 10 has fully distributed oxidant supply, fuelsupply, and/or fuel reformation systems. In the present discussion, a“fully distributed” oxidant supply system and a “fully distributed” fuelsupply system refers to systems in which each SOFC 13 is provided with adesired amount of oxidant/fuel (e.g., an amount necessary for one SOFC13 to produce an electrochemical reaction at the same rate/proportion asthe other SOFCs 13 in the multi-function bundle 10). For example, in oneembodiment, the multi-function bundle may be designed toelectrochemically react approximately 75 to 85% of the fuel supplied toeach SOFC. Accordingly, if each SOFC 13 is supplied with a given amountof fuel, then each SOFC 13 will be supplied with an amount of oxidantnecessary to electrochemically react 75-85% of supplied fuel within theactive region 32, an amount of oxidant to combust the remainder of thefuel in the combustion zone 36, and an amount of excess oxidant tomaintain the desired temperature of the SOFC 13.

Additionally, in the present discussion, a “fully distributed” fuelreformation system refers to a system in which a portion of the fuelreformation system uses a portion of the heat generated by theelectrochemical cell reaction to aid in reformation. For example in thecurrent embodiment, fuel feed tube assemblies 16 may be located amongthe SOFCs 13. As the fuel mixture passes through the fuel feed tubesassemblies 16, it absorbs heat from the electrochemical cell reactionand is reformed into a hydrogen-rich fuel mixture. A fully distributedfuel reformation system may reduce parasitic heat loss, may minimize thecooling impact that the fuel reformation process has on the operation ofthe multi-function bundle 10, and may prevent localized adverse coolingwithin the multi-function bundle 10.

The oxidant supply system may include the oxidant feed tubes 14 and theEAB 18. Oxidant may be distributed, for example, by inserting an oxidantfeed tube 14 within each SOFC 13. FIG. 1C is a detailed view of theclosed end of an SOFC 13 with an oxidant feed tube 14 inserted thereinaccording to one embodiment. The SOFC 13 is comprised of an oxidantelectrode 24, an electrolyte 25, and a fuel electrode 26. Because theouter diameter of the oxidant feed tube 14 is less than the innerdiameter of the SOFC 13, a cavity 28 is formed between the outerdiameter of the oxidant feed tube 14 and the inner diameter of the SOFC13 when the oxidant feed tube 14 is inserted within the SOFC 13. Theoutlet of the oxidant feed tube 14 is near, but not touching, the closedend of the SOFC 13. Thus, oxidant (represented by a series of arrows inFIG. 1C) is able to exit the oxidant feed tube 14, reverse direction,and flow in the cavity 28 between the oxidant feed tube 14 and theoxidant electrode 24. It should be noted that other arrangements may beused while remaining within the scope of the present invention. Forexample, the oxidant feed tube 14 may include a closed end with one ormore ports in its walls to allow oxidant flow.

To prevent lateral vibration of the oxidant feed tube 14, a porouswasher 27 (for example, a short sleeve of Zirconia felt material) may beinstalled inside the cavity 28 formed between the SOFC 13 and theoxidant feed tube 14. In one embodiment, the outer surface of the washer27 bonds to the oxidant electrode 24 during manufacturing and/oroperation. A hole in the center of the washer 27 accommodates and holdsthe oxidant feed tube 14. The porosity of the felt material (e.g., >90%)provides minimal resistance to the flow of the oxidant within the cavity28. Other techniques for preventing lateral vibration between theoxidant feed tube 14 and/or the SOFC 13 may also be used while remainingwithin the scope of the present invention. Additionally, the oxidantfeed tubes 14 may be made of a ceramic material having thermal expansionqualities similar to that of the SOFCs 13 to maintain the clearancebetween the oxidant feed tube 14 and the closed end of the SOFC 13during thermal expansion.

Oxidant is supplied to the oxidant feed tubes 14 via the EAB 18. The EAB18 may include a horizontal flat plate 18 a having individual seats (notshown) for carrying each of the oxidant feed tubes 14. To ensure a tightfitting seal and prevent undesirable movement, each oxidant feed tube 14may be fitted into the individual seats and bonded to the EAB flat plate18 a with ceramic paste. During sintering and/or initial operation, theceramic paste cures to bond the oxidant feed tube 14 to the EAB flatplate 18 a and maintain the seal.

The fuel supply system may include the fuel feed tube assemblies 16 andthe fuel box 19. The fuel reformation system may include a partialreformer and a final reformer. In the current embodiment, the fuel feedtube assemblies 16 may be considered as a part of both the fuel supplysystem and the fuel reformation system. Fuel may be distributed byassociating one or more SOFCs 13 with each fuel feed tube 16.

It should be noted that the EAB 18 may serve multiple roles as part ofthe oxidant distribution system, the support structure, and the exhaustplenum. Likewise, the fuel box 19 may serve a dual role as part of boththe fuel feed supply system and the support structure.

FIG. 2A illustrates a simplified arrangement of a single SOFC 13 of amulti-function bundle 10A according to another embodiment. Asillustrated in FIG. 2A, the support structure of the multi-functionbundle 10A is comprised of a plurality of spacer plates (e.g., 20, 45,46, 47, etc.), supports (e.g., 48, 49, 50, etc.), and a plurality ofalignment pins 51. For simplicity, a single SOFC 13 with an associatedoxidant feed tube 14 is shown located between two fuel feed tubeassemblies 16, however, it should be apparent to one skilled in the artthat the number of SOFCs 13 and fuel feed tube assemblies 16 may bealtered while remaining within the scope of the present invention. TheSOFC 13 passes through an upper cell spacer plate 45 and is carried by acell extender 13 b which is carried by a lower cell spacer plate 46. Theoxidant feed tube 14 is carried by an oxidant feed tube extender 14 awhich is carried by an air tube spacer plate 47.

The air tube spacer plate 47 is supported by a plurality of air chambersupports 50. The air tube spacer plate 47 and air chamber supports 50define an air plenum. The lower cell spacer plate 46 is supported by aplurality of combustion chamber supports 49. The lower cell spacer plate46, combustion chamber supports 49, and the air tube spacer plate 47define a combustion chamber. The upper cell spacer plate 45 is carriedby a plurality of recirc chamber supports 48. The upper cell spacerplate 45, recirc chamber supports 48, and the lower cell spacer plate 46define a recirc plenum. The placement of the air chamber supports 50,combustion chamber supports 49 and recirc chamber supports 48 is setusing alignment pins 51. A plurality of seal locator strips 52 may beused to connect adjacent multifunction bundles 10A. In one embodiment,the seal locator strip 52 has an “H” cross-section that allows it tomate with the edge of the spacer plate 45.

The fuel feed tube assembly 16 passes through a CFF spacer 20 into theactive region 32. The fuel feed tube assembly 16 receives fuel from afuel manifold 54 defined by a reformer box 53 and the CFF spacer 20,among others. Fuel is supplied to the fuel manifold 54 by a fuelmanifold entrance port 55. In the current embodiment, the reformer box53 is nickel impregnated to aid fuel reformation.

The closed end of the SOFC 13 with an oxidant feed tube 14 insertedtherein is similar to that as shown in FIG. 1C. Oxidant is supplied tothe oxidant feed tubes 14 via the air plenum. As discussed above inconjunction with FIG. 2A, each oxidant feed tube 14 may be fitted to anoxidant feed tube extender 14 a (further shown in FIG. 2B) which iscarried by air tube spacer plate 47. Alternatively, the air tube spacerplate 47 may include individual seats (not shown) for carrying each ofthe oxidant feed tubes 14 thus eliminating the need for oxidant feedtube extenders 14 a. To ensure a tight fitting seal and preventundesirable movement, each oxidant feed tube 14 may be fitted into theindividual seats and bonded to the air tube spacer plate 47 with ceramicpaste. During sintering and/or initial operation, the ceramic pastecures to bond the oxidant feed tube 14 to the air tube spacer plate 47and maintain the seal.

FIG. 2B is a detailed view of the open end of the SOFC 13 with the cellextender 13 a attached and the associated oxidant feed tube 14 insertedtherein as illustrated in FIG. 2A. In the current embodiment, cellextender 13 a is a hollow collar through which the oxidant feed tube 14passes. The cell extender 13 a has a shoulder 13 b located on itsoutside diameter, the top of which carries the SOFC 13 and the bottom ofwhich rests on the lower cell spacer plate 46. In addition to carryingthe SOFC 13, the shoulder 13 b provides a seal that prevents oxidant andfuel from reacting at the open end of the SOFC 13.

The outer diameter of the cell extender 13 a (excluding the shoulder 13b) may be less than the diameter of the lower cell spacer plateclearance holes 46 a. Thus, the bottom portion of the cell extender 13 amay fit within the inner diameter of the lower cell spacer plateclearance hole 46 a. Accordingly, the alignment of the SOFC 13 can beadjusted as needed and movement caused by shock and/or thermal expansioncan be accommodated. In the current embodiment, the inner diameter ofthe cell extender 13 a is greater than the outer diameter of the oxidantfeed tube 14 such that oxidant may flow from the cavity 28 into thecombustion zone 36.

As shown in FIG. 2B, the oxidant feed tube 14 may be carried by anoxidant feed tube extender 14 a. In the current embodiment, the oxidantfeed tube extender 14 a is a hollow collar to allow oxidant to flow intothe oxidant feed tube 14. The oxidant feed tube extender 14 a has aninner shoulder 14 b for carrying the oxidant feed tube 14 and an outershoulder 14 c which rests on the air tube spacer plate 47. In additionto carrying the oxidant feed tube 14, the oxidant feed tube extender 14a provides a seal that prevents leakage through the air tube spacerplate clearance holes 47 a.

The outer diameter of the lower portion of the oxidant feed tubeextender 14 a (e.g., below the shoulder 14 c) may be less than thediameter of the air tube spacer plate clearance holes 47 a. Thus, thebottom portion of the oxidant feed tube extender 14 a may fit within theinner diameter of the air tube spacer plate clearance hole 47 a.Accordingly, the alignment of the oxidant feed tube 14 can be adjustedas needed during manufacturing assembly.

As briefly discussed above, the multi-function bundle 10 may have afully distributed final fuel reformation system. For example, final fuelreformation may be distributed by a plurality of fuel feed tubeassemblies 16 which are inserted between and around the SOFCs 13.Partially reformed (i.e., methane-rich) fuel may be supplied to the feedtube assemblies 16 by a manifold 54 contained within the fuel box 19according to one embodiment.

FIGS. 3A and 3B are perspective and end views, respectively, of a fuelfeed tube assembly 16 for the multi-function bundle 10 of FIG. 1Aaccording to one embodiment. The fuel feed tube assembly 16 includes afuel feed tube entrance leg 40, a return leg 41, and (as best seen inFIG. 3B) one or more support fins 42. As best shown in FIG. 3A, the fuelfeed entrance leg 40 may be longer that the fuel feed return leg 41 toaccommodate connection to the fuel supply system.

The flow of fuel within the fuel feed tube assembly 16 is bestillustrated in FIG. 3A. Fuel is supplied to the entrance leg 40 (forexample, from a fuel supply manifold 54 as shown in FIG. 5A) and flowswithin the entrance leg 40 towards the closed end of the fuel feed tubeassembly 16. At the closed end, the fuel exits the entrance leg 40,reverses direction, and flows in the cavity formed between the outsideof the entrance leg 40 and the inside of the return leg 41. The fuelexits the cavity between the entrance leg 40 and the return leg 41 atthe open end, opposite the closed end of the fuel feed tube assembly 16.

In one embodiment, final fuel reformation occurs inside the fuel feedtube assemblies 16. Thus, partially reformed fuel supplied to theentrance leg 40 exits as fully reformed fuel from the open end of thereturn leg 41. To aid the reformation process, one or more components ofthe fuel feed tube assembly 16 may be made from, or coated with, acatalyst material. For example, the surfaces of the entrance leg 40,return leg 41, and the fins 42 may be flash coated with nickel. Itshould be noted that other catalysts may be used while remaining withinthe scope of the present invention. The catalyst choice will dependupon, in part, the fuel to be reformed.

Support fins 42 may insure that the cavity between the outside of theentrance leg 40 and inside of the return leg 41 remains open to allowfuel flow, may enhance the physical strength of the fuel feed assembly16, may aid in reformation (as discussed above), and may facilitate thetransfer of heat between the entrance leg 40 and the return leg 41,among others. As shown in FIG. 3B, the fuel feed tube assembly has fourfins spaced to form four flow paths within the cavity between theoutside of the entrance leg 40 and inside of the return leg 41. Thenumber of fins 42 used, and their relative positioning within the fuelfeed tube assembly 16, may be altered while remaining within the scopeof the present invention. The length of the fins 42 relative to the axisof the entrance leg 40 and return leg 41 may be varied while remainingwithin the scope of the present invention.

The fuel feed tube assembly 16 may function as a counter-flow heatexchanger which improves the thermal distribution within themulti-function bundle 10. For example, the fuel feed tube assembly 16may help reduce the localized cooling impact that the fuel reformationprocess has on the operation of the array of fuel cells 13.

In one embodiment, the fuel feed tube assembly 16 may be extruded as anintegrated unit, however, other methods of construction may be usedwhile remaining within the scope of the present invention. For example,the fuel feed entrance leg 40 may be formed as an elongated sleevehaving an inlet and an outlet and the fuel feed tube return leg 41 maybe formed as an elongated sleeve having an open end and a closed end.The fuel feed tube entrance leg 40 may be nested inside the fuel feedtube return leg 41 to form a fuel flow path similar to that shown inFIG. 3A. The fuel feed tube assembly 16 illustrated in FIGS. 3A and 3Bis substantially cylindrical in shape, however, other shapes may be usedwhile remaining within the scope of the present invention. In addition,tube configurations other than concentric flow passages such asadjoined, side-by-side flow passages (as shown in FIGS. 4A and 4B) maybe used while remaining within the scope of the present invention.

FIGS. 4A and 4B are a perspective view and an end view, respectively, ofa fuel feed tube assembly 16 a for the multi-function bundle 10 of FIG.1A according to another embodiment. The fuel feed tube assembly 16 aincludes a fuel feed tube entrance leg 40, a return leg 41, and (as bestseen in FIG. 4B) one or more divider/support fins 43. As best shown inFIG. 4A, the fuel feed tube entrance leg 40 may be the same length asthe fuel feed tube return leg 41 and the fuel feed tube return leg 41plugged. In an alternative embodiment, the fuel feed entrance leg 40 maybe longer than the fuel feed return leg 41 to accommodate connection tothe fuel supply system.

The flow of fuel within the fuel feed tube assembly 16 a is bestillustrated in FIG. 4A. Fuel is supplied to the entrance leg 40 (forexample, from one embodiment of a fuel supply manifold 54 as shown inFIG. 5A) and flows within the entrance leg 40 towards the closed end ofthe fuel feed tube assembly 16 a. At the closed end, the fuel exits theentrance leg 40, reverses direction, and flows within the return leg 41.As illustrated in FIG. 4A, the top of the fuel feed return leg 41 may besealed. Accordingly, the fuel exits the fuel feed tube assembly 16 a viaone or more fuel feed tube exit ports 44 (e.g., located in the sidewalls of the fuel feed return leg 41, opposite the closed, bottom end ofthe fuel feed tube assembly 16 a). It should be apparent to one skilledin the art that other designs may be used while remaining within thescope of the present invention, for example, the top of the fuel feedreturn leg 41 may be open such that the fuel may flow directly out ofthe top of fuel feed return leg 41.

In one embodiment, final fuel reformation occurs inside the fuel feedtube assemblies 16 a. Thus, partially reformed fuel supplied to theentrance leg 40 exits as fully reformed fuel from the fuel exit ports44. To aid the reformation process, one or more components of the fuelfeed tube assembly 16 a may be made from, or coated with, a catalystmaterial. For example, the surfaces of the entrance leg 40, return leg41, and the divider/support fin 43 may be flash coated with nickel. Itshould be noted that other catalysts may be used while remaining withinthe scope of the present invention. The catalyst choice will dependupon, in part, the fuel to be reformed.

In one embodiment, the fuel feed tube assembly 16 a may be extruded asan integrated unit, however, other methods of construction may be usedwhile remaining within the scope of the present invention. For example,the fuel feed entrance leg 40 and fuel feed return leg 41 may beconstructed separately and then combined to from the fuel feed tubeassembly 16 a. As shown, the fuel feed entrance leg 40 and fuel feedreturn leg 41 are substantially “D-shaped,” such that when combined, thefuel feed tube assembly 16 a illustrated in FIGS. 4A and 4B issubstantially cylindrical in shape. However, other shapes may be usedwhile remaining within the scope of the present invention.

FIGS. 5A-5B are perspective views of the fuel distribution system forthe multi-function bundle 10 according to one embodiment. Referring toFIG. 5A, the fuel feed tube entrance legs 40 for each fuel feed tubeassembly 16, 16 a passes through clearance holes in the bottom of thefuel box 19. The fuel feed tube entrance legs 40 are contained within aspace defined by the fuel box 19 bottom and side walls. A thin layer ofcast insulation material may be used to hold the fuel feed tube entrancelegs 40 in place relative to bottom of the fuel box 19 and may alsoprovide a seal around the entrance legs 40 relative to the clearanceholes in the bottom of the fuel box 19.

A fuel manifold 54 is placed over and connects each of the fuel feedtube entrance legs 40. The fuel manifold 54 may be made from thin-walledtubing. For example, thin-walled nickel tubing may be used to connectthe fuel feed tube entrance legs 40 and to enhance the fuel reformationprocess. The walls of the tubing may be very thin (e.g., approximately1/64 in. thick) to allow the serpentine path of the fuel manifold 54 tobe easily formed. The serpentine path helps to reduce the forces causedby thermal expansion differences between the metal and ceramicmaterials. It should be apparent to one skilled in the art that otherdesigns may be used while remaining within the scope of the presentinvention.

Each fuel manifold 54 may include an associated fuel manifold entranceport 55. In one embodiment, the fuel manifold entrance port 55 extendspast the top of the fuel box's 19 side walls.

Referring to FIG. SB, after the fuel manifold 54 is placed over theprojecting ends of the fuel feed tube entrance legs 40, the fuel feedassembly may be cast in a cement-like insulation material 56. The castinsulation material 56 occupies the space defined by the fuel box's 19bottom and side walls. The cast insulation material 56 provides supportto the multi-function bundle 10 and provides a seal between the manifold54 and the fuel feed entrance legs 40. In one embodiment, a ceramic castinsulation 56 is used. The ceramic cast insulation 56 may be applied toa level flush with the top of the fuel box's 19 side walls such thatonly the fuel manifold entrance port 55 remains exposed. In oneembodiment, the ceramic cast insulation may form the sides of the fuelbox 19.

FIG. 5C is a perspective view of three multi-functional bundles 10joined together in a stack 22. After the cast ceramic insulation 56 isapplied, a row header 57 may be placed over the fuel manifold entranceports 55 of each multi-function bundle 10. Each row header 57 may havean associated row header entrance port 58 for connecting the fueldistribution system to a fuel supply and/or to a recirculation system.In one embodiment, the row header 57 is made from a thin piece of nickeltubing (e.g., to aid in the reformation process) bent in a serpentinepattern (e.g., to accommodate thermal expansion). It should be notedthat other designs for the fuel distribution system may be used whileremaining within the scope of the present invention.

In one embodiment, the fuel feed tube assemblies 16, 16 a may be omittedfrom the multi-function bundle 10. For example, the fuel manifold 54and/or row header 57 may be made from, or coated with, a catalystmaterial to enhance fuel reformation within the manifold 54 and/or rowheader 57. After reformation, the fuel may be distributed directly fromthe fuel manifold 54 to the SOFCs 13 through the holes in the fuel box19. Fuel that does not require reformation may also be supplied directlyto the SOFCs 13 thus eliminating the need to have a catalyst materialpresent in the fuel manifold 54 and/or row header 57.

When the multi-function bundles 10 are placed in a stack 22 (i.e., arestacked next to each other) the edges of the EAB 18, the recirculationbox 17, and the fuel box 19 of a first multi-function bundle 10 contact(and transfer side loads to) the EAB 18, the recirculation box 17, andfuel box 19, respectively, of adjacent multi-function bundles 10. In oneembodiment, the EAB 18, the recirculation box 17, and fuel box 19include tongue-and-groove fits (not shown). The tongue-and groove-fitsensure the relative location of adjacent bundles and enhance thezone-to-zone sealing capability. The tongue-and-groove fits allow thestack 22 to endure large loads (such as those encountered during shockloading), without significant and potentially damaging relativemovement. Large relative movement normal to the axis of thetongue-and-groove is prevented.

The tongue-and-groove fits of the EABs 18 may also form a partial gasseal between adjacent multi-function bundles 10. Although thetongue-and-groove seals may include gaps resulting from assembly andmanufacturing imperfections, they provide a seal that is more effectivethan the conventional controlled leakage seals formed by the clearancebetween SOFCs 13 and the feed through holes in porous spacer boards.

It should be noted that the edges of the recirculation boxes 17 may alsoform a partial gas seal and provide side load support when two or moremulti-function bundles 10 are combined to form a stack 22. However, theedge dimensions and tolerances of the boxes may be designed to ensurethat the EABs 18 provide the predominant side load support (for thelower end of the bundle 10).

FIG. 6A is a perspective view of the multi-function bundle of FIG. 1Aillustrating the different process zones according to one embodiment.For example, fuel distribution zone 30 refers to the region in which thefuel is provided for supply to the fuel cells 13 (for example throughfuel feed tube assemblies 16 shown in FIG. 1A). The active zone 32refers to the region in which the fuel and oxidant combine in anelectrochemical reaction. The recirculation zone 34 refers to the regionin which a portion of the depleted exit fuel mixture is extracted andused, for example, by an external partial reformer before being sentback as partially reformed, methane-rich fuel to the fuel distributionzone 30. The combustion zone 36 refers to the region in which theportion of the fuel mixture remaining after the recirculation zone 34 iscombusted with oxidant entering the combustion zone from the open endsof the SOFCs 13. The oxidant (air) distribution zone 38 refers to thezone in which oxidant is supplied to the oxidant feed tubes 14, forexample, via the EAB 18.

FIG. 6B illustrates a cut-away end view along line 6B-6B of themulti-function bundle 10 with the fuel feed tube assemblies 16 insertedaccording to one embodiment. The fuel feed tube assemblies 16 arelocated between and around the SOFCs 13. Flexible electrical connectors15 may be used to connect the SOFCs 13. For example, a flexibleelectrical connector 15 may be used to connect the fuel electrode 26 ofone SOFC 13 to the fuel electrode 25, or to the cell electricalinterconnect 23, of another SOFC 13. Flexible electrical connectors 15may be made, for example, from a single piece of conductive material(e.g., nickel sheet).

The distribution of fuel feed tube assemblies 16 among the SOFCs 13allows the fuel reformation process to occur in close proximity to theelectrochemical reaction heat source. Thus, parasitic heat loss isgreatly reduced. As the fuel mixture passes through the fuel feed tubesassemblies 16, it absorbs heat from the electrochemical cell reactionand is reformed into a hydrogen-rich fuel mixture.

Returning briefly to FIG. 6A, the basic operation of the multi-functionbundle 10 will be discussed. Oxidant is fed to the oxidant feed tubes 14(located within the SOFCs 13) by the EAB 18. The oxidant enters theoxidant feed tubes 14 and flows the length of the active region 32(i.e., towards the fuel distribution zone 30), exits the oxidant feedtubes 14, reverses direction, and flows inside the cavity 28 between theouter surface of the oxidant feed tube 14 and the inner surface theSOFCs 13 (i.e., towards the recirculation zone 34).

At the same time that oxidant is being fed to the oxidant feed tubes 14,fuel is fed to the outside surface of the SOFCs 13. In one embodiment, amethane rich, partially reformed fuel is distributed to the fuel feedtube assemblies 16 via the fuel manifolds 54. The partially reformedfuel enters the inside of the fuel feed tube entrance leg 40 (i.e., inthe fuel distribution zone 30) and flows the length of the active region32 (i.e., towards the recirculation zone 34). The fuel exits the insideof the fuel feed tube entrance leg 40, reverses direction, and flowsback along the length of the active region 32 (i.e., towards the fueldistribution zone 30) and exits the inside of the fuel feed tube returnleg 41.

As the fuel mixture passes through the fuel feed tube assemblies 16, itabsorbs heat from the electrochemical cell reaction and is fullyreformed into a hydrogen-rich fuel mixture. The fuel feed tubeassemblies 16 allow the final reformation to occur in close proximity tothe electrochemical reaction heat source. Accordingly, heat loss iseliminated for the fuel feed tube assemblies 16 that are surrounded bycells and minimized (through the use of thermal insulation) for the fuelfeed tube assemblies 16 exposed to the periphery. As a resultessentially all of the heat supplied to reform the fuel inside thebundle 10 is available to the cell's electrochemical reaction.

The fully reformed fuel exits the fuel feed tube assemblies 16 in theactive zone 32 near the fuel distribution zone 30. The fully reformedfuel then reverses direction in the active zone and flows (i.e., towardsthe recirculation zone 34) along the outside of the SOFCs where itelectrochemically reacts with oxygen ions that move through the solidelectrolyte 25 as a result of the oxidant flowing within the cavity 28.In one embodiment, approximately 75 to 85% of the available fuel is usedin the electrochemical reaction.

A depleted fuel mixture arrives at the exit of active zone 32 (i.e.,next to the recirculation zone 34). The depleted fuel mixture containsun-reacted fuel and reaction products (for example, a significant amountof water) that may be used to initiate the partial fuel reformation. Thedepleted fuel mixture passes from the active zone 32, through a set ofcontrolled leakage seals (not shown), and into the recirculation zone34. In one embodiment, a portion of the depleted fuel mixture isextracted from the recirculation zone 34, fed to an external partialreformer (not shown) via a re-circulated fuel loop and re-supplied aspartially reformed methane-rich fuel to the fuel distribution zone 30.

In the external partial reformer, raw liquid fuel (such as diesel,kerosene, JP-8, etc.) is vaporized and added to the depleted fuelmixture which contains water vapor to enable steam reformation to occur.After adding vaporized raw fuel, the fuel mixture passes through acatalyst bed where the fuel mixture is partially reformed to become amethane-rich fuel mixture. A fan or blower may be used to overcome thesmall pressure drop through the external partial reformer and pump thepartially reformed, methane-rich fuel mixture back to the fueldistribution zone 30.

The remaining portion of the depleted fuel mixture passes from therecirculation zone 34, through a lower set of controlled leakage seals(not shown), and into the combustion zone 36. Combustion occursimmediately as the fuel mixture combines with depleted oxidant enteringthe combustion zone 36 from the open ends of the SOFCs 13.

It should be noted that some of the heat produced in the combustion zone36 may be absorbed by the oxidant within the oxidant feed tubes 14 whichpass through the combustion zone 36. Thus, heat that would otherwise belost from within the combustion zone 36 may be re-captured.Additionally, the oxidant distribution system may be used to cool themulti-function bundle 10 (i.e., to keep the bundle 10 at the desiredoperating temperature). The total height (fuel distribution zone 30,active region 32, recirculation zone 34, combustion zone 36, and airdistribution zone 38) may be fixed for a particular engine. The ratiobetween the height of the active region 32 and the height of thecombustion zone 36 may be used to establish the maximum power for theengine volume. Unlike typical heat engine practices, the multi-functionbundle 10 does not utilize a recouperator to capture excess heat fromthe exhaust stream (i.e., after the exhaust has left the combustion zone36) to pre-heat the incoming oxidant because doing so would requirelarger air flow passages to accommodate the low density air from therecouperator and thereby make the engine larger to accommodate thelarger flow passages.

In one embodiment, when two or more multi-function bundles 10 arealigned next to each other, the large circular holes in the sides of therecirculation box 17 and the EAB 18 allow the gas mixtures to flowlaterally through the adjacent bundles 10. Thus, three separate flowchannels are formed by the recirculation box 17 and the EAB 18 when thebundles 10 are aligned together. The upper channel (i.e., therecirculation channel) may be connected to a re-circulated fuel loop viaa side port 107 (e.g., as shown in FIG. 15). The intermediate channel(i.e., the exhaust channel) may be connected to a module exhaust linevia a side port similar to side port 107 but located on the oppositeside of the module and at the appropriate height to accommodate thecombustion zone. Similarly, other large circular holes in the lowersides of the EAB 18 allow the oxidant to flow laterally through adjacentbundles 10 resulting in a flow channel when the bundles 10 are alignedtogether. This flow channel may be connected to oxidant supply holes(e.g., as shown in FIG. 13). In another embodiment (for example, thearrangement shown in FIG. 2A), there are no sides; the plates areseparated by pin and support arrangements.

FIGS. 7A and 7B are a perspective view and an end view, respectively, ofa cell-to-cell electrical connector 70 according to one embodiment. FIG.7C is an end view of the electrical connector 70 between two adjacentSOFCs 13. Electrical connector 70 is substantially shaped as anelongated oval (ovals of Cassini) and is sized to fit between adjacentSOFCs 13 in the multi-function bundle 10. As best seen in FIG. 7C,electrical connector 70 may be designed to electrically connect the fuelelectrodes 26 of two adjacent SOFCs 13 or to connect the fuel electrode26 and the electrical interconnect 23 of two adjacent SOFCs 13. Toincrease the contact area between the electrical connector 70 and theSOFCs 13, two opposing surfaces 71 a, 71 b of the electrical connector70 may be shaped to match the outer surface of the SOFC 13.

It should be apparent to those skilled in the art that the shape of thecell-to-cell electrical connector may be altered while remaining withinthe scope of the present invention. For example, FIG. 7D is aperspective view of a cell-to-cell electrical connector 70 having abow-tie-shaped cross section.

FIGS. 8A and 8B are a perspective view and an end view, respectively, ofa cell-to-cell electrical connector 72 according to another embodiment.FIGS. 8C and 8D are an end view and a perspective view, respectively, ofthe electrical connector 72 between several SOFCs 13. Electricalconnector 72 is shaped as an elongated series of curves and is sized tofit between adjacent SOFCs 13 in the multi-function bundle 10. As bestseen in FIG. 8C, electrical connector 72 is designed to electricallyconnect the fuel electrodes 26 of two adjacent SOFCs 13 in the same rowto each other and to the SOFC cell electrical interconnects 23 of twoSOFCs from an adjacent row. To increase the contact area between theelectrical connector 73 and the SOFCs 13, surfaces 73 a, 73 b of theelectrical connector 72 may be shaped to match the outer surface of thefuel electrodes 26 and surfaces 73 c, 73 d may be shaped to match theouter surface of the electrical interconnects 23 of the SOFCs 13.

FIGS. 9A and 9B are a perspective view and an end view, respectively, ofa cell-to-cell electrical connector 74 according to another embodiment.FIG. 9C is an end view of the electrical connector 74 between two SOFCs13. Electrical connector 74 has a curved back and a series ofinterleaved fingers 76 a; 76 b extending from either end. Electricalconnector 74 is elongated and is sized to fit between adjacent SOFCs 13in the multi-function bundle 10. As best seen in FIG. 9C, electricalconnector 74 is designed to electrically connect the fuel electrodes oftwo adjacent SOFCs 13 or to connect the fuel electrode 26 and theelectrical interconnect 23 of two adjacent SOFCs 13. To increase thecontact area between the electrical connector 74 and the SOFCs 13, thesurface 75 a may be shaped to match the outer surface of the SOFC 13 andthe angle between fingers 76 a and 76 b may be selected such that anSOFC 13 fits between the fingers 76 a, 76 b.

FIGS. 10A and 10B are a perspective view and an end view, respectively,of a cell-to-cell electrical connector 77 according to anotherembodiment. FIG. 10C is an end view of the electrical connector 77between two SOFCs 13. Electrical connector 77 is an elongated S-shapethat is sized to fit between adjacent SOFCs 13 in the multi-functionbundle 10. As best seen in FIG. 10C, electrical connector 77 is designedto electrically connect the fuel electrodes 26 of two adjacent SOFCs 13or to connect the fuel electrode 26 and the electrical interconnect 23of two adjacent SOFCs 13. To increase the contact area between theelectrical connector 77 and the SOFCs 13, the surfaces 78 a,78 b may beshaped to match the outer surface of the SOFC 13.

Electrical connectors 70, 72, 74, 77 may be manufactured from a singlesheet of conductive material (e.g., nickel sheets). Portions of materialmay be removed from the sheet to reduce weight without adverselyaffecting the electrical conductivity of the electrical connectors 70,72, 74, 77. The sheet may then be folded, bent, and/or otherwisemanipulated to obtain the desired shape. It should be apparent to oneskilled in the art that other methods and materials may be used tomanufacture the electrical connectors 70, 72, 74, 77 while remainingwithin the scope of the present invention.

FIG. 11 is a cut-away view of the multi-function bundle of FIG. 1Aillustrating the electrical connections using cell-to-cell electricalconnectors 70, 72, 74, 77 according to one embodiment. For example, asseen in FIG. 11, the fuel electrode 26 of SOFC (1, 3) (i.e., the SOFC inrow 1, column 3) may be electrically connected to the fuel electrodes 26of both SOFC (1, 2) (i.e., its left adjacent neighbor) and SOFC (1, 4)(i.e., its right adjacent neighbor) and to the cell electricalinterconnects 23 of SOFCs (2, 2) (2, 3) and (2, 4) (i.e., the SOFCs inrow 2, columns 2, 3, and 4, respectively) by alternatingly stacking theelectrical connectors 72 (for example, as shown in the arrangementillustrated in FIG. 8D).

Additionally, the electrical interconnect 23 of SOFC (5, 2) is connectedto the fuel electrode of SOFC (4, 2) by electrical connector 74, whereasthe fuel electrode 26 of SOFC (5, 2) is connected to the fuel electrodes26 of SOFC (5, 1) and SOFC (5, 3) and to the electrical interconnect 23of SOFC (6, 2) by electrical connector 70. In addition to electricallyconnecting the SOFCs 13, the electrical connectors 70, 72, 74, 77 mayprovide structural support to the SOFCs 13. It should be apparent to oneskilled in the art that the number, type(s), and pattern of electricalconnectors 70, 72, 74, 77 used to connect cells within themulti-function bundle 10 and to connect two or more multi-functionbundles in a stack 22 may be varied while remaining within the scope ofthe present invention.

FIG. 12 illustrates an operational process 60 for assembling themulti-function SOFC bundle of FIG. 1A according to one embodiment. Theassembly of the multi-function bundle 10 according to the currentembodiment may be best understood with reference to FIG. 1B. Inoperation 61, the cell spacer 29 is attached to the primitive bundle 12relative to the open ends of the SOFCs 13.

After the cell spacer is attached in operation 61, the recirculation box17 is attached to the primitive bundle 12 relative to the open ends ofthe SOFCs 13 in operation 62. In the current embodiment, the top of therecirculation box 17 comes in contact with the cell spacer 19 attachedin operation 61.

In operation 63, the oxidant feed tubes 14 are combined with the EAB 18.In one embodiment, an oxidant feed tube extender 14 a is attached (e.g.,with ceramic paste) to the end of each oxidant feed tube 14. The outsidediameter of the lower portion of the oxidant feed tube extender 13 a maybe less than the diameter of the EAB box clearance holes 18 b to allowfor alignment adjustments. Alternatively, the oxidant feed tubes 14 maybe placed into individual seats in the EAB flat plate 18 a. Ceramicpaste may be applied to the oxidant feed tubes 14 or to the seats tobond the oxidant feed tubes 14 to the EAB 18.

After the oxidant feed tubes 14 are combined with the EAB 18 inoperation 63 (and after the recirculation box 17 is attached to theprimitive bundle 12 in operation 62), the oxidant feed tube/EABcombination is attached to the primitive bundle 12 relative to the openends of the SOFCs 13 in operation 64. In the current embodiment, the topof the EAB 18 comes in contact with the bottom of the recirculation box17.

In one embodiment, the recirculation box 17 has a bottom plate 17 a. Thecell spacer 29, the recirculation box bottom plate 17 a, and the EABflat plate 18 a each have a plurality of clearance holes therein. Eachhole in the cell spacer 29 is aligned with a corresponding hole 17 b inthe recirculation box bottom plate 17 a, which is in turn aligned with acorresponding hole 18 b in the EAB flat plate 18 a. In one embodiment,the cell spacer 29, the recirculation box bottom plate 17 a, and the EABflat plate 18 a each have thirty-six holes (i.e., one for each SOFC 13in the primitive bundle 12). Note that other numbers of cells may beused to make the array. The diameter of the holes in the cell spacer 29is preferably slightly larger than the outside diameter of the SOFCs 13.Thus, the ends of the SOFCs 13 in the primitive bundle 12 are alignedwith and passed through the cell spacer 29. The diameter of the holes 17b in the recirculation box bottom plate 17 a is less than the outsidediameter of the SOFCs 13. Thus, the ends of the SOFCs 13 cannot passthrough the recirculation box plate 17 a.

Each SOFC 13 may have an associated cell extender 13 a. The cellextender 13 a may be made from a ceramic material having thermalexpansion characteristics comparable to those of the cell 13 (forexample, zirconia or forsterite) and may be bonded to the end of thecell 13 with ceramic paste. The outside diameter of the cell extender 13a may be less than the diameter of the recirculation box clearance holes46 a to allow for thermal expansion and/or alignment adjustments. Thecell extender 13 a may include a shoulder 13 b having a diameter greaterthan the diameter of the recirculation box clearance holes 46 a. Theshoulder 13 b rests on the recirculation box bottom 17 a and providesload-bearing support for the SOFC 13. The inner diameter of the cellextender 13 a is greater than the outside diameter of the oxidant feedtube 14 such that oxidant can flow in the space defined between the cellextender 13 a and the oxidant feed tube 14.

In addition to providing load support, the cell extender 13 a preventsthe depleted air from reacting with depleted fuel at the open end of theSOFC 13. The cell extender 13 a also protects the open end of the SOFC13 from wearing due to mechanical load and/or burning.

In operation 65, the top of the fuel feed tube assemblies 16 areinserted up through the appropriate holes in the CFF Spacer 20 andinserted into the corresponding appropriate holes in the bottom of thefuel box 19. The bottom of the fuel box 19 includes clearance holes toaccommodate the entrance legs 40 of the fuel feed tube assemblies 16 asdiscussed above in conjunction with FIGS. 5A-5C. Ceramic paste isapplied to the clearance between the fuel feed tube assemblies 16 andthe holes in the bottom of the fuel box 19 to bond the fuel feed tubeassemblies 16 to the fuel box 19.

The fuel box 19 may also have a ceramic fiber board material attached tothe lower surface of its bottom. The ceramic fiber board materialaccommodates small differences in the length of the SOFCs 13 due tomanufacturing irregularities and tolerances.

After the fuel feed tube assemblies 16 are inserted through theappropriate holes in the CFF Spacer 20, through the corresponding holesin the bottom of the fuel box 19, and bonded to the fuel box 19 inoperation 65, this assembly is attached to the primitive bundle 12 inoperation 66.

In operation 66 the CFF spacer 20 is located with the primitive bundle12 relative to the closed ends of the SOFCs 13. In one embodiment, theCFF spacer 20 may be made from a thin sheet of dense ceramic material(zirconia) and may look similar to the head gasket from a conventionalautomotive engine. In one embodiment, the CFF spacer 20 is used tomaintain the spacing between the SOFCs 13 and the fuel feed tubeassemblies 16. The multi-function bundle 10 may be constructed without aCFF spacer 20 while remaining within the scope of the present invention.

In one embodiment, the multi-function bundle 10 may be placed in an ovenand heated to a sintering temperature. The end loading provided by thesintering fixture collapses the ceramic fiber board material of the ofthe fuel box 19 locally to provide custom seating surfaces for eachindividual SOFC 13. In addition, a ceramic paste may be used which cureswith the deformed ceramic fiberboard to maintain a custom fit betweenthe SOFCs 13 and the fuel box 19.

After the fuel feed tube 16 and fuel box 19 combination is attached inoperation 66, the remaining portion of the fuel distribution system isattached in operation 67. In one embodiment, fuel manifolds 54, anassociated fuel manifold entrance port 55, and cast ceramic insulationmay be added as discussed above in conjunction with FIGS. 5A-5B. Shoulda plurality of multi-function bundles 10 be used in a stack 22, a rowheader 57 and row header entrance port 58 may also be added as discussedabove in conjunction with FIG. 5C. An outer shell 21 may also be addedto the multi-function bundle 10 if desired, for example, in the eventbundle-to-bundle separation is needed or the module consists of only onebundle.

FIG. 13 is a cut-away side view of a fuel cell module 88 according toone embodiment. The fuel cell module 88 includes a pressure containmentvessel 90 and a stack 22 of multi-function bundles 10. The pressurecontainment vessel 90 includes a dome 91 and base 92 which may beconnected together, for example, using bolts.

The inner top portion of the dome 91 includes a series of concentricspherical end-rings, where a constant radius of curvature alternatesbetween positive and negative for each progressively larger concentricring. The progressive radial corrugations may result in an averageexternal insulation thickness of 1.0 in. The corrugations also provideenough internal space to accommodate the recirculation flow passageswithout sacrificing active length.

In one embodiment, the dome's 91 configuration (with two radialcorrugations (four diametral)) is similar to the ends of a conventionalsoup can. The dome 91 is designed to avoid bulging outward during normaloperation. However during an overpressure condition, the dome 91 canbulge outward providing a built-in mechanism to rapidly relieve theexcess pressure and absorb excess energy. Although the dome 91 may haveto be replaced after such an incident, a potentially dangerous explosioncan be avoided.

Referring briefly to FIG. 14, the base 92 includes a recirculationentrance port feed through 93, a recirculation exit port feed through94, an oxidant inlet port feed through 95, an exhaust port feed through96, a positive electric terminal feed through 97, and a negativeelectric terminal feed through 98, among others. The base 92 may alsoinclude one or more module mounts 87 for securing the containment vessel90, for example, to a vehicle chassis.

The base 92 serves as a fixture to provide a suitable foundation forassembling the multi-function bundles 10 into a stack 22. Returning toFIG. 13, the base 92 may include a rigid base plate 92 a and a sphericalouter wall 92 b. Preferably, interactions between the stack 22 and thecontainment vessel 90 are limited to the stack's 22 contact with thebase plate 92 a. As a result, the upper end of the stack 22 can grow andshrink thermally within the pressure containment vessel 90 withoutconstraint from the dome 91. The rigid base plate 92 a provides a flatinternal load bearing surface which may be supported by the sphericalouter wall 92 b. For example, the spherical outer wall 92 b may includea ledge around its inner circular perimeter on which the rigid baseplate 92 a may rest. The rigid base plate 92 a may form a false bottomrelative to the spherical outer wall 92 b. Thus, the rigid base plate 92a takes advantage of the rigidity of the outer spherical wall 92 b whileproviding a means for oxidant flow distribution throughout the fuel cellmodule 88. With proper oxidant flow distribution, a uniform temperaturemay be maintained throughout the whole base plate 92 and thermal stresscan be essentially eliminated. Additionally, the whole base plate 92thermally isolates the bottom of the stack 22 from the externalenvironment.

The rigid base plate 92 a offers a flat reference plane during assemblyof the stack 22 and remains flat throughout the operational range of thefuel cell module 88. Thus, the rigid base plate 92 a preventsundesirable movement of the stack 22. For example, the rigid base plate92 a prevents excessive relative motion (which would result in surfacefretting) between adjacent multi-function bundles 10 in the stack 22during both normal operating conditions and during unusual conditionssuch as shock loading when the body forces can vary by as much as anorder of magnitude.

As illustrated in FIG. 13, rigid base plate 92 a is a circular platethat rests on the ledge around the inner circular perimeter of thespherical outer wall 92 b. In addition, several supports 92 c projectupward from the spherical outer wall 92 b to help support the rigid baseplate 92 a. In one embodiment, the rigid base plate 92 a may beconfigured from webbed beam structures such as an “I” beam, whichprovide high strength per weight. The small “I” beams may be placedside-by-side and joined together to form a honeycomb structure.

FIG. 13 also illustrates the process gas flows throughout the fuel cellmodule 88 with respect to different activity zones. The small arrowsrepresent the flow of various process gas. In one embodiment, the rigidbase plate 92 a includes three different rings of holes 92 d to allowoxidant to move upward from the oxidant inlet port feed through 95 andinto the EABs 18 of the multi-function bundles 10 of stack 22. Each EAB18 has an open bottom to accommodate the oxidant flowing up through theholes in the rigid base plate 92 a. The EABs 18 also have holes aroundthe four sides to allow oxidant to flow laterally from one EAB 18 toanother EAB 18.

As seen in FIG. 13, oxidant enters the fuel cell module 88 through theoxidant inlet port feed through 95 in the center of the base plate 92 a.In one embodiment, the oxidant is distributed laterally in the airdistribution zone 38 to all of the multi-function bundles 10 via thecircular holes in the sides of the EABs 18. The oxidant enters theoxidant feed tubes 14 in each multi-function bundle 10 through circularholes in the EAB plate 18 a. The fuel enters the fuel cell module 88through the recirculation entrance port feed through 93 and isdistributed to the row header entrance ports 58. The fuel then passesthrough the row headers 57, is distributed to the fuel manifold entranceports 55, enters the fuel manifolds 54, and is distributed to the fuelfeed tube assemblies 16.

After the fuel and oxidant electrochemically react in the active zone32, the depleted fuel mixture arrives at the exit of active zone 32(i.e., next to the recirculation zone 34). The depleted fuel mixturecontains un-reacted fuel and reaction products (for example, asignificant amount of water). The depleted fuel mixture passes from theactive zone 32, through a set of controlled leakage seals (not shown),and into the recirculation zone 34. A portion of the depleted fuelmixture is extracted from the recirculation zone 36 via therecirculation exit port feed through 94 and fed to an external partialreformer via a re-circulated fuel loop and back to the recirculationentrance port feed through 93.

The remaining portion of the depleted fuel mixture passes from therecirculation zone 34, through a lower set of controlled leakage seals(not shown), and into the combustion zone 36. Combustion occursimmediately as the fuel mixture combines with depleted oxidant enteringthe combustion zone 36 from the open ends of the SOFCs 13. Thecombustion exhaust is then expelled from the fuel cell module 88 via theexhaust port feed through 96.

The electricity generated by the stack 22 of multi-function bundles 10may be routed via leads (not shown) to an electric drive (not shown) viapositive electric terminal feed through 97 and a negative electricterminal feed through 98. The electric drive may be used, for example,to drive the wheels of a truck or other vehicle.

To reduce overall weight, the dome 91 is not used to provide structuralsupport to the stack 22, nor as a means to lift the fuel cell module 88.However, the dome's 91 flange, when properly bolted to the base plate 92a , provides a small amount of structural rigidity to the base plate 92a. The stack 22 is designed to be self-supporting when combined with thebase 92, and therefore requires no support from (nor interaction with)the dome 91. The fuel cell module 88 may be lifted either from below(for example, by a fork-lift applied underneath the base plate to thethick ring support section), or from above (for example, using a specialfixture that hooks into lifting holes 101 drilled into the base 92).

Little or no relative movement between the bottom of the stack 22 (i.e.,the EABs 18) and the rigid base plate 92 a is expected during normaloperating conditions. However, in the event of unusual conditions suchas an unusually large temperature differential, the stack 22 is allowedto move relative to the rigid base plate 92 a without resulting inadverse loads. To control relative movement, the stack 22 may be pinnedto the rigid base plate 92 a.

The pin locations according to one embodiment are best seen in FIG. 14which is a partial top view of the fuel cell module 88 of FIG. 13mounted on a truck chassis 89. A reference pin 99 is located next to apositive electric terminal feed through 97. All relative movementbetween the stack 22 and the rigid base plate 92 a will occur withrespect to this reference pin 99. Two additional pins, calledsingle-plane location pins 100, are also used to control stack 22movement relative to the rigid base plate 92 a. As illustrated in FIG.14, a single-plane location pin 100 located next to a negative electricterminal feed through 98 (near the exhaust port feed through 96) allowsthe stack 22 to move relative to the rigid base plate 92 a in a firstdirection. Likewise, a single-plane location pin 100 located next to therecirculation exit port feed through 94 allows the stack 22 to moverelative to the rigid base plate 92 a in another direction.

In one embodiment, all three location pins (the reference pin 99 and thetwo single-plane location pins 100) are rigid parts of the base plate 92a. The reference pin 99 fits into a tight clearance hole in an EAB endpiece 102. The single-plane location pins 100 will each fit into tightclearance slots; the pin 100 next to the negative electric terminal feedthrough 98 only allows relative movement in the lateral front-to-backdirection while the other pin 100 (next to the recirculation exit portfeed through 94) only allows relative movement in the lateralside-to-side direction.

In addition to controlling the location of the stack 22 relative to therigid base plate 92 a, the location pins 100 may act as shear pins whichprevent the stack 22 from undesirable movement during unusual shockloading. These pins 100 may be designed, for example, to accommodate alateral shock load of 10 g's including a safety factor of 2×.

FIG. 15 is an isometric view of a stack 22 of multi-function fuel cellbundles 10 and associated support structures for the fuel cell module 88of FIG. 13 according to one embodiment. The stack 22 consists of thedesired number of rows of multi-function bundles 10 placed next to eachother in the proper order, surrounded at the bottom by EAB end/sidepieces 102, and surrounded at the middle and top by riser end/sidepieces 103. A lower band 104 surrounds and holds the EAB end/side pieces102 and an upper band 105 surrounds and holds the riser end/side pieces103.

As illustrated in FIG. 15, the EAB end/side pieces 102 surround the EABs18 and all together, form a structural support base for the stack 22allowing it to make uniform contact with the rigid base plate 92 a. Theinterface contact between the EAB end/side pieces 102 and the rigid baseplate 92 a provides a seal around the oxidant distribution zone of thestack 22. The seal is the result of intimate contact between the topsurface of the base plate 92 a and the bottom surface of the EABend/side pieces 102.

The riser end/side pieces 103 are located directly above the EABend/side pieces 102. The risers 103 may be made from a low-strength(low-density) ceramic material that provides thermal insulation. Theadditional height of the EAB end pieces 102 (relative to the EAB sidepieces 102) is set to accommodate the process gas flow ducts since theriser material is unable to provide any significant structural strength.For example, FIG. 15 shows an outline (dashed lines) of an exhaust port107 in the EAB end piece 102. The exhaust port 107 aligns with theexhaust port feed though 96 of the base 92. A recirculation exit port(not shown) is configured similarly in the EAB end piece 102 at theopposite end of the stack 22.

The stack 22 may be held together as a unit by two circumferentialbands. In one embodiment, an upper band 105 may be at the height of atongue-and-groove location on the fuel box 19 and the lower band 104 isat the height of the EAB 18 tongue-and-groove locations. As previouslymentioned in addition to ensuring the relative location of adjacentbundles, the tongue-and-groove fits also enhance the zone-to-zonesealing capability. The tongue-and-groove fits allow the stack 22 toendure large loads (such as those encountered during shock loading),without significant and potentially damaging relative movement. Largerelative movement normal to the axis of the tongue-and-groove isprevented. However, very small relative movement normal to the axis ofthe tongue-and-groove can occur when the edge friction forces areovercome, but the amount of relative movement is limited to the stack-upof the movements of the “tongues” within the clearance of the “grooves”.

The clamping force provided by the bands 104, 105 holds the edgesurfaces of the multi-function bundles 10 in contact with each other andthereby allows the stack 22 to act kinematically as a single unit. As aresult, the force required to resist lateral shock loads is a constantregardless of the number of bundles 10 in the stack 22 (althoughadditional rows of bundles increase the mass, they also proportionatelyincrease the effective moment arm).

Although there are similarities, the upper band 105 may be significantlydifferent than the lower band 104. Both upper 105 and lower 104 bandsmust accommodate hang-up and friction loads resulting from relativemovement between the bottom of the stack 22 and the rigid base plate 92a, between the tongue-and-groove elements, and between the band 104; 105and the material underneath the band (e.g., EAB side piece 102, riserend/side piece 103, etc.). In addition, both upper 105 and lower 104bands must accommodate lateral shock loads and thermal expansiondifferences during both normal and start-up operating conditions of thefuel cell module 88.

Because the bottom of the stack 22 is pinned to the base plate 92 a, theshock loading on the lower band 104 is significantly greater than thatof the upper band 105. Also, the flexibility (inverse of stiffness) ofthe upper band 105 may be significantly greater than that of the lowerband 104 to accommodate the low-strength characteristics of the risers103 that are sandwiched between the upper band 105 and the fuel boxes19.

In one embodiment, the lower band 104 may be 1.25 in high by 0.172 inthick. The overall thickness of the band may be achieved by combiningeleven layers, each 1/64 in thick, to provide a combined thickness of11/64 (0.172 in). The 1.25 in height is selected to be 0.25 in greaterthan the height of the EAB side pieces 102, thereby providing a smalllip around the outer perimeter of the EAB side pieces 102 to help locatethe riser side pieces 103. The lower band 104 may be made from inconel718 which may be the same as the material of the EAB end/side pieces 102to eliminate different thermal expansion rates. The cross-sectional areaof the lower band 104 may be set to allow the band 104 to accommodate alarge lateral shock load, for example, 10 g's. In addition, thecross-sectional area of the clamping-bolt (not shown) that holds theends of the lower band 104 together may be the same ( 9/16-18 bolt).

During assembly and normal operating conditions, the temperature of thelower band 104 will be equal to the temperature of the EAB end/sidepieces 102, therefore, there will be no thermal growth difference. Thus,lower band 104 flexibility is not needed for assembly and normaloperating conditions. However, during start-up conditions, there is asignificant thermal gradient across the EAB end/side pieces 102resulting in a difference in temperature (and thermal growth) betweenthe EAB end/side pieces 102 and the lower band 104. The lower band 104may yield from stress due to thermal growth difference when the averagetemperature of the EAB end/side pieces 102 is 800F greater than theaverage temperature of the lower band 104.

To make sure the average temperature of the EAB end/side pieces 102cannot exceed the lower band 104 average temperature by 800 F, a smallbleed-off groove 106 is machined in the outer surface of the EABend/side pieces 102, underneath the band 104. Referring briefly to FIG.16, heated oxidant is supplied to the bleed-off groove 106 via twooxidant distribution zone links 110. The oxidant flows through thebleed-off groove 106 and exits via an exhaust link 11 connected to theexhaust system. In one embodiment, the bleed-off groove 106 may be 0.25inches wide by 0.25 inches deep. At the recirculation end of the stack22, the groove 106 is linked to the oxidant distribution zone by twoseparate 0.25 inch diameter oxidant distribution zone links 110 drilledthrough the EAB end piece 102. At the exhaust end of the stack 22, thegroove 106 is linked to the exhaust by a 0.35 inch diameter exhaust link111 in the EAB end piece 102. FIG. 11 shows the overall layout of thebleed-off groove 106 arrangement for the lower band 104.

In one embodiment, the lower band 104 may be made from a high strengthsteel (for example, inconel 718) whereas the EAB 18 and EAB end/sidepieces 102 may be made from a ceramic material (for example, alumina)having a thermal expansion rate significantly lower than that of thelower band 104. Clamping bolts (not shown) may be used to hold the endsof the lower band 104 together and provide sufficient preload on thelower band 104 to maintain the desired clamping load during assembly,normal operating conditions, and start-up/shut-down conditions. Thesmall bleed-off groove 106 may be used to provide oxidant flow tomaintain the temperature of the EAB end/side pieces 102 at a temperaturenear the temperature of the lower band 104.

The above-described embodiments of the invention are intended to beillustrative only. Numerous alternative embodiments may be devised bythose skilled in the art without departing from the scope of thefollowing claims. For example, the electrodes of the SOFCs 13 may bereversed such that the oxidant electrode forms the outside surface andthe fuel electrode 26 forms the inside surface of the SOFC 13. With afew modifications, the fuel supply system and the oxidant supply systemmay be reversed in this embodiment. More specifically, the feed tubesinserted into each SOFCs 13 are used to supply fuel to the fuelelectrode. Fuel is supplied to these feed tubes using the EAB. Thesefeed tubes may include a catalyst material to aid fuel reformation.Additionally, the feed tube assemblies inserted between each fuel cellare used to supply oxidant to the oxidant electrodes. Oxidant issupplied to these feed tube assemblies using the fuel manifolds. Thesefeed tube assemblies do not need a catalyst material.

1-100. (canceled)
 101. A fuel cell assembly comprising one or more fuel cell bundles, each fuel cell bundle comprising: an array of elongated tubular fuel cells comprising a first row of spaced apart, elongated tubular fuel cells; a second row of spaced apart, elongated tubular fuel cells; and a plurality of elongated electrical connectors, wherein each electrical connector has at least two curved surfaces, a first contact for coupling with a first fuel cell and a second contact for coupling with a second cell, wherein each of said first and second contacts defines a plurality of slots and wherein each of said electrical connectors is disposed between at least two of said elongated tubular fuel cells; an oxidant supply system; a fuel supply system; a fuel reformation system; and a support structure for integrating as a bundle said fuel cells, said oxidant supply system, said fuel supply system, and said fuel reformation system.
 102. The fuel cell assembly of claim 101 wherein each of said plurality of elongated electrical connectors has a substantially S-shaped cross-section and each of said first and second contacts comprises a concave outer surface.
 103. The fuel cell assembly of claim 101 wherein each of said plurality of elongated electrical connectors comprises one or more materials selected from the group consisting of: nickel sheet, copper sheet and aluminum sheet.
 104. The fuel cell assembly of claim 101 wherein one or more of said plurality of elongated electrical connectors further comprises third and fourth contacts and provides an electrical connection between four fuel cells with two of said four fuel cells being from said first row and two from said second row.
 105. The fuel cell assembly of claim 101 wherein said support structure includes at least one of an exhaust/air distribution box, a recirculation box, a fuel box, a cell spacer, and a fuel cell and fuel feed spacer.
 106. The fuel cell assembly of claim 105 wherein at least one of said exhaust/air distribution box, said recirculation box, said fuel box, said cell spacer, and said fuel cell and fuel feed spacer includes a tongue-and-groove connector.
 107. A fuel cell assembly comprising one or more fuel cell bundles, each fuel cell bundle comprising: an array of elongated tubular fuel cells comprising a first row of spaced apart, elongated tubular fuel cells; a second row of spaced apart, elongated tubular fuel cells; and a plurality of elongated electrical connectors each having at least two angled surfaces, a first contact for coupling with a first fuel cell and a second contact for coupling with a second cell, wherein at least one of said first and second contacts defines a plurality of slots or apertures between, and wherein each of said electrical connectors is disposed between at least two of said elongated tubular fuel cells; an oxidant supply system; a fuel supply system; a fuel reformation system; and a support structure for integrating as a bundle said fuel cells, said oxidant supply system, said fuel supply system, and said fuel reformation system.
 108. The fuel cell assembly of claim 107 wherein each of said plurality of elongated electrical connectors defines a generally hollow, three dimensional shape.
 109. The fuel cell assembly of claim 107 wherein each of said plurality of elongated electrical connectors has a generally bow-tie shaped cross section.
 110. The fuel cell assembly of claim 107 wherein each of said plurality of elongated electrical connectors has a generally rectangular shaped cross section.
 111. The fuel cell assembly of claim 107 wherein said fuel supply system further comprises: a fuel box having a plurality of holes therein for distributing fuel to said plurality of fuel cells; a manifold for supplying fuel to said fuel box, said manifold having an entrance port; and a cast insulation material operable to seal said manifold within said fuel box.
 112. The fuel cell assembly of claim 107 wherein said support includes at least one of an upper cell spacer plate, a lower cell spacer plate, an air tube spacer plate, chamber supports, a reformer box, seal locator strips, and a cell and fuel feed spacer.
 113. A fuel cell assembly comprising one or more fuel cell bundles, each fuel cell bundle comprising: an array of elongated tubular fuel cells comprising a first row of spaced apart, elongated tubular fuel cells; a second row of spaced apart, elongated tubular fuel cells; and a plurality of elongated electrical connectors each having at plurality of curved surfaces, and a plurality of contacts for coupling with one of said fuel cells, wherein at least one of said plurality of contacts defines a plurality of slots or apertures, and wherein each of said electrical connectors is disposed between at least two of said elongated tubular fuel cells; an oxidant supply system; a fuel supply system; a fuel reformation system; and a support structure for integrating as a bundle said fuel cells, said oxidant supply system, said fuel supply system, and said fuel reformation system.
 114. The fuel cell assembly of claim 113 wherein each of said plurality of elongated electrical connectors defines a generally hollow, three dimensional shape.
 115. The fuel cell assembly of claim 113 wherein each of said plurality of contacts is curved to couple with the curvature of an outside surface of one of said fuel cells.
 116. The fuel cell assembly of claim 113 wherein said fuel supply system comprises a plurality of fuel feed tube assemblies each comprising an inlet leg in fluid communication with an outlet leg to form a flow path.
 117. The fuel cell assembly of claim 113 wherein said support structure includes at least one of an exhaust/air distribution box, a recirculation box, a fuel box, a cell spacer, and a cell and fuel feed spacer attached to said plurality of fuel cells. 